Question

Why does Mercury have a convex meniscus?

Answer 1

Hint:A meniscus can ascend or descend. It all depends on if the liquid's molecules are more attracted to the substance outside or to itself. The justification for this is often attributed to cohesion and adhesion.

Complete answer:
The convex meniscus is formed when the cohesive forces are stronger, (i.e.) attractive forces between molecules of the same substance whereas the concave meniscus is formed when the adhesive forces are stronger, (i.e.), attraction between molecules of a different substance.

When we put one end of a capillary tube into a liquid, it is found that the liquid rises into the capillary tube up to a certain height. It is thanks to the inward pull of physical phenomenon working on the surface which pushes the liquid into the capillary.A curved surface is formed in the capillary tube known as the meniscus.There are two sorts of attractive forces acting between the molecules:
- Cohesive and
- Adhesive forces.

Let us consider two liquids:
1. Water and
2. Mercury
In the case taken during a glass tube, the adhesive forces are stronger (force of attraction between water molecules and glass molecules) than the cohesive forces hence concave meniscus is made. Whereas just in the case of mercury the cohesive forces are the stronger force of attraction between mercury molecules is stronger hence, the convex meniscus is made

Note:Mercury is an exception where the cohesive forces are stronger but generally in the case of all other liquids adhesive forces are stronger so generally, we see concave meniscus in all liquids Meniscus tends to travel up and down which is dependent upon the molecules of the liquid.